Fiber-optic communication is widely used in applications such as telecommunications and communication within large data centers. Because of attenuation losses associated with using shorter optical wavelengths most fiber-optic communication uses optical wavelengths of 800 nm and longer. Commonly used transmission windows exist between 1260 nm and 1675 nm. A main component of optical receivers used in fiber-optic communication system is the photo detector, usually in the form of a photodiode (PD) or avalanche photodiode (APD).
High-quality low-noise APDs can be made from silicon. However, while silicon will absorb light in the visible and near infrared range, it becomes more transparent at longer optical wavelengths. Silicon PDs and APDs can be made for optical wavelengths of 800 nm and longer by increasing the thickness of the absorption “I” region of the device. FIG. 2 is a cross section of a conventional PIN photodiode 200, where “d” is the length of the absorption “I” region 220. FIGS. 3A and 3B show bandwidth and quantum efficiency a conventional silicon photodiode with a 30-micron diameter at 850 nm optical wavelength. As can be seen, in order to obtain a quantum efficiency of 90% the thickness “d” of the “I” region is over 30 microns. This leads to a maximum bandwidth of less than 2.5 Gb/s, which is too low for many current and future telecom and data center applications.
To avoid the inherent problem that silicon PDs and APDs have with longer wavelengths and higher bandwidths, other materials are used. Germanium (Ge) detects infrared out to a wavelength of 1700 nm, but has relatively high multiplication noise. InGaAs can detect out to longer than 1600 nm, and has less multiplication noise than Ge but still has far greater noise than silicon. InGaAs is known to be used as the absorption region of a heterostructure diode, most typically involving InP as a substrate and as a multiplication layer. This material system is compatible with an absorption window of roughly 900 to 1700 nm. However both InGaAs and Ge devices are relatively expensive and have relatively high multiplication noise when compared with silicon.
The subject matter claimed herein is not limited to embodiments that solve any specific disadvantages or that operate only in environments such as those described above. Rather, this background Is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.